551 install problemsSupport

Hi friends, i m using samsung gt 551 from one and half years now and have been constantly facing some or the other problem.
now suddenly i m facing lots of problem together
1) i cant connect my phone to my pc through usb, the phone is getting charged but it doesnt show the usb symbol and neither asks weather i want to connect through usb or kies.
2) i cant install any app (.apk file) through my sd card. it shows installing but nothing happens.
3) i cant install anything from the market because the install and download option doesn't appear
4) in the cell phone's application manager, it is not showing the size of any application. It just prompts computing and then nothing happens

i have tried rebooting
i have reset my phone to factory default
i have also tried connecting my phone to other usb ports and other computers too, but nothing changes

Get the phone flashed to stock firmware .
Samsung firmwares have a roughly life span of 4-6 months
Then it starts degrading of sorts (no scientific reason to support ,just experience )
Factory reset soesnt help since it just flashes /data which is pointless
One of the reason every reputed manufacturer releases a firmware update regularly .
It sort of flushes the system
However Samsung has not released a update for some regions like (Asia ) since one and a half year .